The third generation partnership project known as 3GPP has developed and standardised an Internet Protocol Multimedia Sub-system (IMS) to provide a multi-media and call control service architecture. The service architecture is supported by a real-time capable Universal Mobile Telecommunications System (UMTS) communicating data in the form of Internet Protocol (IP) packets. IMS provides a basis for service provision and development of new services and is envisioned as a standardised convergence platform, which enables integration of real time multi-media services with non-real time services and person-to-machine communications. In addition, IMS provides the ability to modify a media type, which is active during a multimedia session. For instance, video media can be added during a communications session which was originally established for an audio only communication.
Co-pending European Patent application number 02293276.8 discloses a mobility manager, which can initiate and direct hand-over execution of a mobile terminal from one access network to another, in accordance with information received from a network operator, the network itself and mobile terminals and a network policy provided by a policy enforcer. The mobility manager provides a facility for enabling a network operator to adapt a service being provided by an application program in accordance with a relative ability of an access network to which the mobile terminal is to be re-affiliated to support the service, before or after the re-affiliation has occurred. To this end, there is also disclosed a communication protocol between an application server and a mobility manager located in a core network of a mobile communications network.
WO 01/58177 discloses a method for controlling hand-over of a mobile terminal conducting a communications session in a mobile communications network. The method includes receiving a trigger indicating a requirement for hand-over, testing the conditions for hand-over with respect to a network policy for communicating and controlling the hand-over in accordance with the hand-over requirement with respect to the network communications policy.